Quick PHP implementation of AWS Signature Version 4 docs example request

awsSignatureVersion4.php

<?php

// See docs here: https://docs.aws.amazon.com/general/latest/gr/sigv4_signing.html
// running example here: https://3v4l.org/E3oBG

$body = '';
$bodyHash = hash('sha256', $body);

$canonicalRequest = <<<HEREDOC
GET
/
Action=ListUsers&Version=2010-05-08
content-type:application/x-www-form-urlencoded; charset=utf-8
host:iam.amazonaws.com
x-amz-date:20150830T123600Z

content-type;host;x-amz-date
$bodyHash
HEREDOC;

$canonicalRequestHash = hash('sha256', $canonicalRequest);

$stringToSign = <<<HEREDOC
AWS4-HMAC-SHA256
20150830T123600Z
20150830/us-east-1/iam/aws4_request
$canonicalRequestHash
HEREDOC;

$region = 'us-east-1';
$service = 'iam';
$date = '20150830';
$kSecret = 'wJalrXUtnFEMI/K7MDENG+bPxRfiCYEXAMPLEKEY';


$kDate = hash_hmac('sha256', $date, 'AWS4' . $kSecret, TRUE);
$kRegion = hash_hmac('sha256', $region, $kDate, TRUE);
$kService = hash_hmac('sha256', $service, $kRegion, TRUE);
$kSigning = hash_hmac('sha256', "aws4_request", $kService, TRUE);

$signature = hash_hmac('sha256', $stringToSign, $kSigning);

echo $signature;